1. Field of the Invention
The invention relates generally to processes and apparatus for removing volatile components from materials such as solutions, dispersions, slurries, emulsions, and pastes. More particularly, the invention relates to processes for removing volatile components from materials with an apparatus having a plurality of channels.
2. Description of Related Technology
Detergent products contain surface active ingredients (sometimes referred to as "detergent active ingredients" or "detergent actives"), which may be neutralized salts of acids produced, for example, by sulfating or sulfonating C.sub.8 -C.sub.20 organic materials and, preferably, C.sub.11 -C.sub.18 organic materials, such as, for example, fatty alcohols, ethoxylated fatty alcohols, alkyl benzenes, alpha olefins, methyl esters, and alkyl phenol ethoxylates. The process of making detergent actives from the acid form is typically performed in a solvent, such as water and/or alcohol. The resulting detergent material may be a paste, a solution, or a slurry of various components. (The term detergent "paste" as used hereinafter is meant to include detergent solutions, slurries and pastes). Final detergent products are made from such detergent pastes.
One of the most common detergent products, a laundry powder, is conventionally prepared by mixing a paste containing the desirable detergent actives, and other by-products, various salts, detergent builders and water to form a slurry with about 25 weight percent (wt. %) to about 60 wt. % water, more preferably, from about 30 wt. % to about 45 wt. % water. Preferably, the paste ingredients are compatible with each other and are insensitive to the drying process.
A conventional method of producing a detergent powder by removing solvents from a detergent paste involves spraying the detergent paste counter-currently or co-currently with hot air in a spray-drying tower. This process most often yields a free-flowing, low density (approximately 0.3 specific gravity) granule having a moisture content of 2 wt. % to 12 wt. %. Since solvent removal in the spray-drying process requires heating and exhausting large amounts of air, the process tends to be energy intensive. Some conventional spray-drying processes also cause detergent actives and heat-sensitive builders to undergo physical and chemical degradation because of the severe drying conditions in certain regions of the spray-drying tower. Environmental concerns are yet another concern with such conventional processes. Exhaust gasses produced by drying a detergent paste in conventional spray drying processes may contain volatile organic materials and particulates requiring downstream pollution control measures. A better approach for making laundry detergent powder formulated products is to dry only those components of the formulation that require water (or other solvents) to be added to them during the manufacturing process. This typically would include the detergent actives, but other ingredients, such as sodium silicate for example, may also be admixed in the form of an aqueous (or solvent) solution. The dry actives mixture resulting from such a process step can then be agglomerated with the other dry salts and builders present in the formulation, using small amounts of suitable liquid agglomerating agents. Such an agglomeration step is accomplished in various types of commercial equipment, including fluid beds and tumbling drums, some of which may be equipped with mechanical agitators. To assist in this process approach, it is desirable to produce the detergent actives in as concentrated a form as possible. Drying of detergent actives, alone or in combination with other liquid ingredients of a product formulation, is performed using conventional spray drying processes with the aforementioned disadvantages and problems. Other commercial techniques have been practiced, such as drying with "wiped film" evaporators or drying on a heated surface of rotating drums (drum drying). The equipment is expensive, limited in production capacity, and is maintenance intensive. Some of these processing techniques will not handle highly concentrated pastes, and consequentially will be less energy efficient.
While problems encountered when drying detergent pastes in traditional drying equipment have been discussed thus far, it is noted that similar problems are encountered when drying a variety of materials, for example, organic and inorganic pigments, inorganic salts, food-stuffs and pharmaceuticals, which may be in the form of a solution, slurry or paste and may be heat sensitive. Also traditional drying equipment may not be suitable in situations wherein only selected components or selected amounts of components are to be removed from a composition, resulting in, for example, a more concentrated solution, or a solution or paste from which a particular undesirable component has been removed.
Thus, it would be desirable to provide a method and apparatus capable of removing volatile components from a variety of compositions that avoids the problems encountered by the prior art. More specifically, it would be desirable to provide a method and apparatus for producing a pure, dry detergent from a concentrated detergent paste. Furthermore, it would be desirable to provide a simple method and apparatus capable of making dry detergents on a large volume basis, which reduces the environmental concerns and high energy costs discussed above and does not lead to detergent active degradation. Also desirable would be a method and apparatus for removing volatile components from a wide range of materials which become soft and flowable at elevated temperatures. Furthermore, it would be desirable to provide a method and apparatus for drying a large number of organic and inorganic compounds that have no tendency to cake during the drying step, and that form discrete solid particles when dried. Still further, it would be desirable to provide a method and apparatus for drying highly concentrated viscous pastes, which are not possible to handle in some of the prior art processes.